Adhesion promoter and coating composition for adhesion to olefinic substrates

ABSTRACT

An adhesion promoter, a coating composition containing the adhesion promoter, and a method for preparing the adhesion promoter and coating. The adhesion promoter is an olefin based polymer having at least one amine containing compound. The amine may be used as a catalyst for the coating.

FIELD

This present disclosure relates to adhesion promoters and curablecoating compositions, especially compositions that are applied overolefinic substrates such as thermoplastic polyolefin (TPO); and a methodof making the coatings.

BACKGROUND

Adhesion additives are known throughout the automotive coatingsindustry. Adhesion additives are often used as components in primersurfacers, or other intermediate coating compositions, to promoteadhesion between a substrate and a topcoat system for an automobile,such as a topcoat system including a flexible basecoat and flexibleclearcoat. In general, plastic substrates may be coated with curable, orthermosettable, coating compositions. Color-plus-clear compositecoatings have been particularly useful as topcoats for which exceptionalgloss, depth of color, distinctness of image, or special metalliceffects are desired.

As largely used in primer surfacers, adhesion additives are typicallysolvent-borne primer surfacers, but may also be used in water-borneprimer surfacers, that are applied to a bumper, i.e., facie, or othertrim component as the substrate. Typically, these substrates are made upof thermoplastic polyolefin (TPO), and without the inclusion of anadhesion copolymer in an intermediate solvent-borne primer surfacerlayer, the topcoat system may delaminate from the TPO substrate.

One kind of adhesion additive includes olefin-based based polymers orcopolymers that have an olefin block that is substantially saturated andat least one (poly)ester or (poly)ether block. The olefin-based blockpolymer or copolymer is typically present in an organic solvent such asxylene, toluene, and the like. The individual components of the adhesioncopolymers, i.e., the olefin-based polymer or block copolymer,frequently settle out into the organic solvent. This settling rendersthe adhesion composition unstable, i.e., having poor shelf stability,and therefore not suitable for use as a component of a solvent borneprimer.

It has been found that the conductivity of wet paint and dry filmcoatings influences the transfer efficiency of adhesion promoters andtopcoats, respectively. In order to obtain high transfer efficiency ofan adhesion promoter on a typical plastic component with a very highresistivity, large amounts of polar solvents, often in an amount fromabout 5 to 25% based on formula weight, have typically been used toadjust the conductivity.

It is desirable to provide a coating composition without the addition oflarge amounts of polar solvents, that yet has a more stable adhesionpromoter component of the coating composition that provides improvedphysical properties, including improved adhesion under harsh testingconditions and improved conductivity to allow for more efficientelectrostatic spray applications.

SUMMARY

The present disclosure provides an adhesion promoting composition thatincludes an olefin based polymer or block copolymer, or a mixture ofthese, having at least one amine containing compound in addition toother adhesion promoting functional groups that do not react with aprincipal resin or crosslinking resin in a coating composition. Thepresent disclosure also provides a coating composition containing theadhesion promoter.

In various embodiments, the amine containing compound is selected fromthe group consisting of dimethylaminoethanol and aminomethylpropanol.The amine containing compound is typically present in an amount fromabout 1% to about 2% by weight based on total vehicle weight. Theolefin-based polymer may include a carboxyl functional adhesioncopolymer and at least one functional group selected from the groupconsisting of hydroxyl, thiol, amide, carbamate, urea, acid, phenol, andcombinations thereof. The olefin-based polymer is typically present inan amount from about 0.01% to about 30% by weight based on total vehicleweight.

Coating compositions used with the adhesion promoter of the presentdisclosure may provide a wet paint resistivity of less than about 1.5Mohms, or less than about 1 Mohms. The coating compositions may providea dry film resistivity of less than about 0.02 Mohms, or less than about0.01 Mohms.

Methods for preparing the adhesion promoter and the coating containingthe adhesion additive are also provided. A method of improving thetransfer efficiency of a topcoat layer to a primed component includesapplying a carboxyl functional olefin based polymer composition to asubstrate to provide a primed component and electrostatically applying acoating composition comprising principal resin and crosslinker to theprimed component to form a topcoat layer. The carboxyl functionalpolymer is neutralized with at least one amine containing compound toform a salted carboxyl functional polymer. Additionally, in certainembodiments, the amine containing compound may be used as a catalyst inthe formation of the coating composition.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no wayintended to limit the disclosure, its application, or uses.

“A” and “an” as used herein indicate “at least one” of the item ispresent; a plurality of such items may be present, when possible.“About” when applied to values indicates that the calculation or themeasurement allows some slight imprecision in the value (with someapproach to exactness in the value; approximately or reasonably close tothe value; nearly). If, for some reason, the imprecision provided by“about” is not otherwise understood in the art with this ordinarymeaning, then “about” as used herein indicates a possible variation ofup to 5% in the value. As used throughout, ranges are used as a shorthand for describing each and every value that is within the range. Anyvalue within the range may be selected as the terminus of the range.

Adhesion promoters are typically solventborne adhesion promoting primersthat are designed to be applied over a plastic substrate, such as TPO,to provide a primer layer between the plastic substrate and a topcoatlayer. As is known in the art, adhesion promoters help to improve theadhesion of the topcoat to the plastic. The present disclosure providesan adhesion promoting composition that includes an olefin-based polymeror block copolymer, or a mixture of these, including at least one aminegroup containing compound in addition to other adhesion promotingfunctional groups that do not react with a principal resin orcrosslinking resin in a coating composition. As used herein, the term“principal resin” is used with reference to the main resin(s) that mayprovide film forming aspects. In certain instances, the principal resinmay be the resin present in the largest amount. The adhesion promoter ofthe present disclosure preferably includes at least one carboxylfunctional adhesion promoting polymer. A small amount of the amine maybe provided to internally salt the adhesion promoting polymer. Byneutralizing the carboxyl groups of the polymer with an amine to form asalt, it has been found that the resistivity of a composition containingthe neutralized polymer is lowered due to the high conductivity of thesalt (as compared with a composition coating the un-salted carboxylpolymer).

More specifically, it has been found that the addition of the amineimproves (i.e., lowers) both the wet paint resistivity and the dry filmresistivity. Lower wet paint resistivity provides a higher transferefficiency of the adhesion promoter to a part via an electrostatic sprayapplication. Lower dry film resistivity improves the transfer efficiencyof the topcoat layer to a plastic part for a more efficient paintingprocess. With the adhesion promoter of the present disclosure, largeamounts of polar solvents may not have to be used to adjust theconductivity, leading to more stable coating formulations. Additionally,it has been found that the amine-containing compound may be used as acatalyst in the formation of the coating composition layer. As anon-limiting example, when used with a two-component urethane topcoat,the amine could volatize from the adhesion promoter or primer layer andserve as a catalyst for an isocyanate-alcohol reaction in curing thetopcoat layer.

The adhesion promoter of the present disclosure may comprise at leastone olefin-based polymer or copolymer having a functionality thereonthat is substantially non-reactive with the film forming components of acoating composition when subjected to curing conditions. Theolefin-based polymer or copolymer of the invention may be prepared fromsaturated or substantially saturated polyolefin preferably having anumber average molecular weight of from about 1,000 up to about 5,000,more preferably from about 1,000 up to about 3,500, and even morepreferably from about 1,500 up to about 3,500. The adhesion promoter isused in a coating to promote adhesion to a substrate, preferably a TPOsubstrate. As used herein, the olefin based adhesion promoter refers toboth the olefin based polymer and olefin based block copolymer.

The olefin-based polymer may be produced by hydrogenation of apolyfunctional polydiene polymer. The polydiene polymer may have anyfunctional group that is an active hydrogen donor, or a group that isconverted to an active hydrogen donor and is not reactive withfunctionality on a principal or crosslinking resin in a coatingcomposition containing the olefin based polymer. Polycarboxylated andpolyhydroxylated polydiene polymers can most easily utilized due totheir commercial availability. Polyhydroxylated polydiene polymers maybe produced by anionic polymerization of monomers such as isoprene orbutadiene and capping the polymerization product with alkylene oxide andmethanol, as described in U.S. Pat. Nos. 4,039,593, 5,376,745,5,486,570, and Reissue 27,145, each of which is incorporated herein byreference in their entirety. The polyhydroxylated polydiene polymer issubstantially saturated by hydrogenation of the double bonds that is atleast 90 percent, preferably at least 95% and even more preferablyessentially 100% complete to form the hydroxyl-functional olefinpolymer. The hydroxyl equivalent weight of the hydroxyl-functionalsaturated olefin polymer may be from about 500 to about 20,000. Thehydroxy functional olefin-based polymer thus prepared is then reactedwith a compound reactive with the hydroxyl functionality to provide afunctionality that is non-reactive with a principal resin orcrosslinking resin in a coating composition. Such non-reactivefunctionality includes thiol, acid, epoxy and hydrogen donor and/oracceptor functionality.

Alternatively, the olefin-based polymer may comprise a block copolymerthat has an olefin block and at least one (poly)ester, (poly)urethane or(poly)ether block. By the terms “(poly)ester block” “(poly)urethaneblock” and (poly)ether block” it is meant that the base polyolefinmaterial is modified with one or more monomer units through formationof, respectively, ester, urethane or ether linkages. For purposes of thepresent disclosure, “(poly)ester block” has a special meaning that, inthe case of two or more monomer units, the monomer units arepredominantly, preferably exclusively, arranged in head-to-taillinkages.

The olefin-based polymer may be prepared by reacting ahydroxyl-functional, saturated or substantially saturated olefin polymerwith a chain-extension reagent that is reactive with hydroxyl groups andwill polymerize in a head-to-tail arrangement of monomer units. Suchchain-extension reagents include, without limitation, lactones, hydroxycarboxylic acids, oxirane-functional materials such as alkylene oxides,and combinations of these. Examples of chain-extension reagents arelactones and alkylene oxides. Specific examples of these include εcaprolactone, ethylene oxide, and propylene oxide. The hydroxy groups onthe olefin-based block polymer thus formed are in turn reacted with acompound to provide adhesion-promoting functional groups that do notreact with a principal resin or a crosslinking resin of a coatingcomposition.

Preferably, the block polymer has one block of the olefin material towhich is attached one or more of the (poly)ester, (poly)urethane and/or(poly)ether blocks. In one embodiment, the olefin-based block copolymerof the disclosure may be represented by a structure selected fromA-[(B—F_(n))]_(m) and A-F_(n) in which A represents an olefin block, Brepresents a (poly)ester, (poly)urethane or (poly)ether block orcombinations thereof, F is a functional group that does not react with aprincipal resin or crosslinker in the coating composition and m is onaverage from about 0.7 to about 10, alternatively from about 1.7 toabout 2.2 or from about 1.9 to about 2, and n is on average from 2 to 4.

The A block may be a saturated or substantially saturated olefinpolymer. In one embodiment, the A block is substantially linear. Ingeneral, about 15% or less of the carbons of the A block should bependant to the olefin polymer backbone. Preferably 10% or less, morepreferably 8% or less of the carbons of the A block should be pendant tothe olefin polymer backbone. Each B block preferably may contain, onaverage, from about 0.5 to about 25 monomer units, more preferably onaverage from about 2 to about 10, and even more preferably on averagefrom about 2 to about 6 monomer units per hydroxyl group of theunmodified olefin block. The monomer units may be the same or there maybe different monomer units in a single (poly)ester, (poly)urethane or(poly)ether block. For example, a (poly)ether block may have one or moreethylene oxide units and one or more propylene oxide units.

In both the olefin polymer and block copolymer, the hydroxyl-functionalolefin polymer utilized is preferably a hydroxyl-functional hydrogenatedpolymer of butadiene with ethylene, propylene, 1,2 butene, andcombinations of these. The olefin polymers may have a number averagemolecular weight of preferably from about 1,000 to about 10,000, morepreferably from about 1,000 to about 5,000, even more preferably fromabout 1,000 up to about 3,500, and still more preferably from about1,500 up to about 3,500. The olefin polymer also preferably has at leastone hydroxyl group on average per molecule. The olefin polymer may havefrom about 0.7 to about 10 hydroxyl groups on average per molecule, morepreferably from about 1.7 to about 2.2 hydroxyl groups on average permolecule, and still more preferably about 2 hydroxyl groups on averageper molecule. The hydroxyl-functional olefin polymer may have terminalhydroxyl groups and a hydroxyl equivalent weight of from about 1,000 toabout 3,000. Molecular weight polydispersities of less than about 1.2,particularly about 1.1 or less, are preferred for these materials.

The olefin polymer is preferably a low molecular weightpoly(ethylene/butylene) polymer having at least one hydroxyl group. Inanother embodiment, the polyolefin polyol is a hydrogenatedpolybutadiene. Such hydrogenated polyolefin polyols are those availableunder the trademark POLYTAIL™ from Mitsubishi Chemical Corporation,Specialty Chemicals Company, Tokyo, Japan, including POLYTAIL™ H.

In one embodiment, a block copolymer is formed from thehydroxy-functional olefin polymer by reaction with a lactone or ahydroxy carboxylic acid to form an olefin-based polymer having(poly)ester end blocks. Lactones that may be ring opened by an activehydrogen are well-known in the art. Examples of suitable lactonesinclude, without limitation, ε-caprolactone, γ-caprolactone,β-butyrolactone, β-propriolactone, γ-butyrolactone,α-methylα-butyrolactone, β-methyl-γ-butyrolactone, γ-valerolactone,δ-valerolactone, γ-decanolactone, δ-decanolactone, γ-nonanoic lactone,γ-octanoic lactone, and combinations of these.

The lactone ring-opening reaction is typically conducted under elevatedtemperature (e.g., 80-150° C.). When the reactants are liquids a solventis not necessary. However, a solvent may be useful in promoting goodconditions for the reaction even when the reactants are liquid. Anynon-reactive solvent may be used, including both polar and nonpolarorganic solvents. Examples of useful solvents include, withoutlimitation, Solvesso 100 (a mixed hydrocarbon solvent), Solvesso 150,(mixed hydrocarbon solvent), naptha, methyl propyl ketone, methyl ethylketone, methyl isobutyl ketone toluene, xylene, and the like andcombinations of such solvents. A catalyst may be utilized. Usefulcatalysts include, without limitation, proton acids (e.g., octanoicacid, Amberlyst® 15 (Rohm & Haas)), and tin catalysts (e.g., stannousoctoate). Alternatively, the reaction may be initiated by forming asodium salt of the hydroxyl group on the molecules that will react withthe lactone ring.

A hydroxy carboxylic acid can also be used instead of a lactone or incombination with a lactone as the compound that reacts with thehydroxyl-functional olefin polymer to provide ester blocks. Usefulhydroxy carboxylic acids include, without limitation,dimethylhydroxypropionic acid, hydroxy stearic acid, tartaric acid,lactic acid, 2-hydroxyethyl benzoic acid, N-(2-hydroxyethyl)ethylenediamine triacetic acid, and combinations of these.

The reaction may be conducted under typical esterification conditions,for example at temperatures from room temperature up to about 150° C.,and with catalysts such as, for example, calcium octoate, metalhydroxides like potassium hydroxide, Group I or Group II metals such assodium or lithium, metal carbonates such as potassium carbonate ormagnesium carbonate (which may be enhanced by use in combination withcrown ethers), organometallic oxides and esters such as dibutyl tinoxide, stannous octoate, and calcium octoate, metal alkoxides such assodium methoxide and aluminum tripropoxide, protic acids like sulfuricacid. The reaction may also be conducted at room temperature with apolymer-supported catalyst such as Amerlyst-15® (available from Rohm &Haas).

While polyester segments may likewise be produced with dihydroxy anddicarboxylic acid compounds, it may be preferred to avoid such compoundsbecause of the tendency of reactions involving these compounds toincrease the polydispersity of the resulting block copolymer. If used,these compounds should be used in limited amounts and preferablyemployed only after the lactone or hydroxy carboxylic acid reactantshave fully reacted.

The reaction with the lactone or hydroxy carboxylic acid or oxiranecompounds adds at least one monomer unit as the B block and preferablyprovides chain extension of the olefin polymer. In particular, the(poly)ester and/or (poly)ether block is thought to affect the polarityand effective reactivity of the end group functionality during curing ofthe coating.

The (poly)ester and/or (poly)ether block also makes the olefin-basedblock copolymer more compatible with components of a typical curablecoating composition. The amount of the extension depends upon the molesof the alkylene oxide, lactone, and/or hydroxy carboxylic acid availablefor reaction. The relative amounts of the olefin polymer and thealkylene oxide, lactone, and/or hydroxy acid may be varied to controlthe degree of chain extension. The reaction of the lactone ring, oxiranering, and/or hydroxy carboxylic acid with a hydroxyl group results inthe formation of an ether or ester and a new resulting hydroxyl groupthat can then react with another available monomer, thus providing thedesired chain extension. In the present disclosure, the equivalents ofoxirane, lactone, and/or hydroxy carboxylic acid for each equivalent ofhydroxyl on the olefin polymer are from about 0.5 to about 25, or fromabout 1 to about 10, or from about 2 to about 6. In a specificembodiment about 2.5 equivalents of lactone are reacted for eachequivalent of hydroxyl on the olefin polymer.

In another embodiment of the disclosure, a polyolefin having terminalhydroxyl groups is reacted with an oxirane-containing compound toproduce (poly)ether endblocks. The oxirane-containing compound ispreferably an alkylene oxide or cyclic ether, especially preferably acompound selected from ethylene oxide, propylene oxide, butylene oxide,tetrahydrofuran, and combinations of these. Alkylene oxide polymersegments include, without limitation, the polymerization products ofethylene oxide, propylene oxide, 1,2-cyclohexene oxide, 1-butene oxide,2-butene oxide, 1-hexene oxide, tert-butylethylene oxide, phenylglycidyl ether, 1-decene oxide, isobutylene oxide, cyclopentene oxide,1-pentene oxide, and combinations of these. The hydroxyl group of theolefin-based polymer functions as initiator for the base-catalyzedalkylene oxide polymerization. The polymerization may be carried out,for example, by charging the hydroxyl-terminated olefin polymer and acatalytic amount of caustic, such as potassium hydroxide, sodiummethoxide, or potassium tert-butoxide, and adding the alkylene oxide ata sufficient rate to keep the monomer available for reaction. Two ormore different alkylene oxide monomers may be randomly copolymerized bycoincidental addition and polymerized in blocks by sequential addition.

Tetrahydrofuran polymerizes under known conditions to form repeatingunits [CH₂CH₂CH₂CH₂O]—. Tetrahydrofuran may be polymerized by a cationicring-opening reaction using such counterions as SbF₆ ⁻, AsF₆ ⁻, PF₆ ⁻,SbCl₆ ⁻, BF₄ ⁻, CF₃SO₃ ⁻, FSO₃ ⁻, and ClO₄ ⁻. Initiation is by formationof a tertiary oxonium ion. The polytetrahydrofuran segment may beprepared as a “living polymer” and terminated by reaction with thehydroxyl group of the olefin polymer.

The non-reactive functionality on either type of polyolefin polymer maybe provided for example by reacting the hydroxyl functionality on theolefin polymer with an anhydride functional compound to provide an acidfunctionality. Suitable anhydride functional compounds include cyclicanhydrides derived from polycarboxylic acids wherein at least two of theacid groups are located beta or gamma (1, 2 or 1,3) to form the cyclicanhydride though a dehydration reaction yielding the cyclic anhydrideand water. The cyclic anhydride may also include other acid groups orhalogen groups or aliphatic, olinic (unsaturated carbon chains),cycloaliphatic or aromatic side groups of chain lengths between 1 and 18carbons. These must not interfere with formation of the cyclicanhydride. Examples of these include trimelaic anhydride,hexahyrophthalic, phthalic anhydride, tetrahydrophthallic anhydride,hexahydrophthalic anhydride, methyl hexahydrophthalic anhydride, maleicanhydride, succinic anhydride, glutaric anhydride,2-dodecen-1-ylsuccinic anhydride, and dodecenylsuccinic anhydride.Mixtures of anhydrides may also be used. Thiol functionality may beobtained by forming a polyolefin halide and then reacting the halidewith sodium hydrogen sulfide.

In another embodiment, a hydroxy functional olefin polymer may bereacted with an isocyanate functional pre-polymer. The isocyanatefunctional pre-polymer may be made by the reaction of a polyfunctionalisocyanate with less than a stoichiometric amount of a difunctionalchain extension material having functional groups selected from thegroup consisting of polyols, polyamines, hydroxy amines and combinationsthereof. Alternatively, or in addition, the polyfunctional isocyanatemay be reacted with one or more capping agents that comprise a hydroxyor an amine group and an additional functional group that is essentiallyinert to the isocyanate under the reaction conditions. The amount ofcapping agent used must be less than the stoichiometric amount ofavailable isocyanate. To prevent unwanted molecular weight growth and/orgellation, the polyisocyanates such as diisocyanates including, but notlimited to isophorone diisocyanate, hexane diisocyanate, toluenediisocyanate are effective. In most cases, the chain extension agentswill be difunctional. Non-limiting examples of chain extension agentsare 2-ethyl-hexane-1,3-diol, 1,6-hexanediamine, and 6-amino-hexane-1-ol.These chain extension agents may be extended prior to reaction with thepolyisocyanate. A non-limiting example is the reaction of 1,6-hexanediolwith a lactone. Non-limiting examples of capping agents are hydroxyalkyl carbamates such as hydroxy propyl carbamate, 1-hydroxy-pentanoicacid and 1-hydroxy-butyl amide. These capping agents may be extended byreaction with lactones.

The olefin-based polymer of the adhesion promoter may be used in acoating composition in an amount from between about 0.01 and about 30%by weight based on the total vehicle weight. Alternatively, the adhesionpromoter polymer may be used in an amount from between about 3 to about30% by weight, or between about 5 and about 20% by weight based on totalvehicle weight. “Vehicle,” as used herein, is understood to be theresinous and polymer components of the coating composition, whichincludes film forming resins and polymers, crosslinkers, other reactivecomponents such as the olefin-based block copolymer, the chlorinatedpolyolefin, and other reactive or nonreactive resinous or polymericcomponents such as acrylic microgels.

While not intending to be bound by theory, it is believed that themechanism that results in adhesion of the coating to the substrateinvolves a migration of the olefin-based polymer or block copolymer tothe olefinic or TPO substrate interface and an interaction with theolefinic or TPO substrate. It is believed that the migration and/orinteraction is facilitated by application of heat, such as the heatapplied to cure the coating composition. It is thought that thenon-reactivity of the functional groups on the olefin-based polymer orcopolymer toward the principal resin and crosslinker leaves thefunctionality available to provide adhesion between the coating and theolefinic or TPO substrate. It is believed that the hydrogendonor/acceptor nature of the groups enhances the adhesive properties ofthe substituted polyolefin polymer. Since the groups are essentiallyinert to reaction with a principal resin or a crosslinking resin in acoating composition, the groups remain essentially unreacted and in tactin the final coating system. By “essentially unreacted” or “essentiallyinert”, is meant that only trace amounts or less than 8% and preferablyless than 1% of the functional groups may react with principal resin orcrosslinker.

The coating compositions of the disclosure may contain a wide variety offilm-forming resins. At least one crosslinkable resin is typicallyincluded. The resin may be self-crosslinking, but typically a coatingcomposition includes one or more crosslinking agents reactive with thefunctional groups on the film-forming resin. Film-forming resins forcoating compositions typically have such functional groups as, forexample, without limitation, hydroxyl, carboxyl, carbamate, urea,epoxide (oxirane), primary or secondary amine, amido, thiol, silane, andso on and combinations of these. The film-forming resin may be any ofthose used in coating compositions including, without limitation,acrylic polymers, vinyl polymers, polyurethanes, polyesters (includingalkyds), polyethers, epoxies, and combinations and graft copolymers ofthese. Also included are polymers in which one kind of polymer is usedas a monomer in forming another, such as a polyester-polyurethane,acrylic-polyurethane, or a polyether-polyurethane in which a dihydroxyfunctional polyester, acrylic polymer, or polyether is used as a monomerin the urethane polymerization reaction. Useful film-forming resinsinclude acrylic, polyurethane and polyester polymers, including alkydsand mixtures of any of these. Useful acrylic resins include those havinga hydroxyl number of between 95 and 225. In the case of waterbornecompositions, the film-forming resin is emulsified or dispersed in thewater. In one embodiment, a waterborne coating composition includes botha polyurethane and an acrylic resin. Many references describefilm-forming polymers for curable coating compositions and so thesematerials do not need to be described in further detail here.

Film-forming resins may be included in amounts of from about 5 to about99%, preferably from about 20 to about 80% of the total solid vehicle ofthe coating composition.

When the coating composition includes a curing agent, or crosslinker,the crosslinker is non-reactive with the olefin-based polymer or blockcopolymer under normal curing conditions. The curing agent has, onaverage, at least about two crosslinking functional groups. Suitablecuring agents include, without limitation, materials having activemethylol or methylalkoxy groups, such as aminoplast crosslinking agentsor phenol/formaldehyde adducts, curing agents that have isocyanategroups, particularly blocked isocyanate curing agents; curing agentshaving epoxide groups; and combinations of these. Examples of specificcuring agent compounds include melamine formaldehyde resins (includingmonomeric or polymeric melamine resin and partially or fully alkylatedmelamine resin), blocked or unblocked polyisocyanates (e.g., toluenediisocyanate, MDI, isophorone diisocyanate, hexamethylene diisocyanate,and isocyanurate trimers of these, which may be blocked for example withalcohols or oximes), urea resins (e.g., methylol ureas such as ureaformaldehyde resin, alkoxy ureas such as butylated urea formaldehyderesin), polyanhydrides (e.g., polysuccinic anhydride), polysiloxanes(e.g., trimethoxy siloxane), and combinations of these. Unblockedpolyisocyanate curing agents are usually formulated in two-package (2K)compositions, in which the curing agent and the film-forming polymer (inthis case, at least the block copolymer) are mixed only shortly beforeapplication and because the mixture has a relatively short pot life. Thecuring agent may be combinations of these, particularly combinationsthat include aminoplast crosslinking agents. Aminoplast resins includemelamine formaldehyde resins or urea formaldehyde resins.

In various embodiments of the present disclosure, an amine may be usedas a catalyst for the coating layer. For example, in the case of a twocomponent urethane topcoat, an amine can volatize and provide a catalystfor the R—NCO+R′—OH reaction. The amine salt of this polymer could alsobe used to salt the polymer into water and form a waterborn adhesioncopolymer. In various embodiments, an amine containing compound for thepresent disclosure is selected from the group consisting ofdimethylaminoethanol and aminomethylpropanol. The amine containingcompound is typically present in an amount from about 1% to about 2% byweight based on total vehicle weight.

The functionality on the olefin-based polymeric adhesion promoterfunctionality is preferably selected so that it is not reactive withfunctional groups on either the principal resin or crosslinker in thecoating composition. The functionality may be selected from the groupconsisting of hydroxyl, acid, thiol, carbamate, urea, amine, phenol andamide groups and mixtures thereof, depending on its inertness to thefunctionality of the principal resin and crosslinker.

For example, where an isocyanate crosslinker or resin is used with ahydroxyl functional resin, the functional group on the adhesion promotermay be selected from the group consisting of amides, phenol, carbamates,acid and mixtures thereof. The functional group on the olefin-basedadhesion promoter may be obtained for example, by reacting a hydroxylfunctional olefinic polymer produced by hydrogenation of apolyhydroxylated polydiene polymer with a compound to provide acid,thiol, carbamate, urea, amine phenol, or amide functionality that doesnot react with the hydroxyl functionality on the principal resin or theisocyanate functionality on the crosslinker.

For example, when an epoxy functional principal resin and acidcrosslinker or acid functional principal resin with epoxy crosslinker,or an ultraviolet radiation curable principal resin and crosslinker areused, the functionality on the adhesion promoter may be selected fromthe group consisting of alcohols, amides, carbamates, phenol and ureaand mixtures thereof.

Aminoplast resins such as melamine formaldehyde resins or ureaformaldehyde resins are specific example of crosslinkers for resinshaving hydroxyl, carbamate, and/or urea functional groups. Where thecrosslinker is aminoplast, the functionality on the adhesion promoter isacid or thiol.

A coating composition comprising the olefin-based polymer or blockcopolymer adhesion promoter may further include other components,including and without limitation for example, chlorinated polyolefin,additional adhesion promoters, catalysts suitable for reaction of theparticular crosslinker, solvents including water and organic solvents,surfactants, stabilizers, matting agents, wetting agents, rheologycontrol agents, dispersing agents, adhesion promoters, pigments,fillers, uv absorbers, hindered amine light stabilizers, siliconeadditives, customary coatings additives, and combinations of these.Suitable pigments and fillers include, without limitation, conductivepigments, including conductive carbon black pigments and conductivetitanium dioxide pigments; non-conductive titanium dioxide and carbonpigments, graphite, magnesium silicate, ferric oxide, aluminum silicate,barium sulfate, aluminum phosphomolybdate, aluminum pigments, and colorpigments. The pigments and, optionally, fillers are typically includedat a pigment to binder ratio of from about 0.1 to about 0.6, preferablyfrom about 0.1 to about 0.25.

The adhesion promoter olefin-based polymer of the disclosure may beapplied directly to a substrate or combined with a chlorinatedpolyolefin adhesion promoter for direct application to a substrate, orthe olefin-based polymer may be used as a component of a coatingcomposition. The adhesion promoter is particularly useful for olefinicsubstrates such as TPO to provide excellent adhesion of subsequentcoating layers to the substrates. Use of the olefin polymer improvescoating performance following gasoline immersion testing.

Where the adhesion promoter olefin-based polymer is combined with achlorinated polyolefin good adhesion following exposure to humiditytesting is obtained. Some non-limiting examples of chlorinatedpolyolefins may be found in U.S. Pat. Nos. 4,683,264; 5,102,944; and5,319,032. Chlorinated polyolefins are known in the art and arecommercially available form various companies, including Nippon Paper,Tokyo, Japan, under the designation Superchlon; Eastman ChemicalCompany, Kingsport, Tenn. under the designation CPO; and Toyo KaseiKogyo Company, Ltd., Osaka, Japan under the designation Hardlen.Examples of non-chlorinated adhesion promoters include AP-550-1 fromEastman Chemical.

The coating compositions of the disclosure may comprise chlorinatedpolyolefin in an amount between 0 and about 25% by weight, and in someembodiments between about 0.001% and about 25% by weight, or betweenabout 1.0 and 15.0% by weight, or between 1.0 and 10.0% by weight, basedon total vehicle weight.

In one embodiment, the coating comprises only a solution or dispersionthat includes only or essentially only the olefin-based block copolymerand chlorinated polyolefin as the vehicle components. In thisembodiment, it is preferred to first apply the adhesion promoterdirectly to the, plastic substrate and then to apply a layer of acoating composition. Applying coating layers “wet-on-wet” is well knownin the art.

For this embodiment of the adhesion promoter, the applied adhesionpromoter may be either coated “wet on wet” with one or more coatingcompositions and then all layers cured together, or the adhesionpromoter layer may be partially or fully cured before being coated withany additional coating layers. Curing under any of these conditionsallows subsequent coating layer(s) to be applied electrostatically whenthe adhesion promoter is utilized with or without conductive pigments,for example as conductive carbon black or conductive titanium dioxide,according to methods known in the art.

The use of the adhesion promoter polymer or copolymer of the presentdisclosure increases the conductivity of the primer system and reducesthe amount used or eliminates the conductive pigment used in the coatingcomposition. Improved conductivity increases topcoat transfer efficiencyin electrostatic spray systems.

Curing the adhesion promoter layer before applying an additional coatinglayer may allow the subsequent coating layer to be appliedelectrostatically when the adhesion promoter is formulated with aconductive pigment such as conductive carbon black or conductivetitanium dioxide, according to methods known in the art.

The adhesion promoter polymer may be added to a variety of coatingcompositions to produce coating compositions that have excellentadhesion to plastic substrates, particularly to olefinic substrates,including TPO. Compositions in which the combination of the polymericadhesion promoter may be used include primers, one-layer topcoats,basecoats, and clearcoats.

The adhesion promoter or coating composition used in the practice of thedisclosure may include a catalyst to enhance the cure reaction. Forexample, when aminoplast compounds, especially monomeric melamines, areused as a curing agent, a strong acid catalyst may be utilized toenhance the cure reaction. Such catalysts are well-known in the art andinclude, without limitation, p-toluenesulfonic acid, dinonylnaphthalenedisulfonic acid, dodecylbenzenesulfonic acid, phenyl acid phosphate,monobutyl maleate, butyl phosphate, and hydroxy phosphate ester. Strongacid catalysts are often blocked, e.g. with an amine. Other catalyststhat may be useful in the composition of the disclosure include Lewisacids, zinc salts, and tin salts.

A solvent may optionally be included in the adhesion promoter or coatingcomposition used in the practice of the present disclosure, andpreferably at least one solvent is included. In general, the solvent maybe any organic solvent and/or water. It is possible to use one or moreof a broad variety of organic solvents. The organic solvent or solventsare selected according to the usual methods and with the usualconsiderations. In the present disclosure, the solvent is present in thecoating composition in an amount of from about 0.01 weight percent toabout 99 weight percent. Typically, in organic solventborne compositionssolvent is present from about 5 weight percent to about 70 weightpercent, and for topcoat compositions from about 10 weight percent toabout 50 weight percent. In a preferred embodiment, the coating has lessthan 4% HAPS.

In another embodiment, the solvent is water or a mixture of water withany of the typical co-solvents employed in aqueous dispersions. When theolefin-block copolymer is to be used in a waterborne composition, it isadvantageous to include in the block copolymer at least one polyethyleneoxide segment or ionizable group to aid in dispersing the material. Whenmodified with a polyethylene oxide segment or ionizable group, the blockcopolymer of the disclosure may be dispersed in water, optionally withother components (crosslinkers, additives, etc.) and then applied as anadhesion promoter or added to an aqueous coating composition as anaqueous dispersion of the block copolymer. Alternatively, the blockcopolymer may be blended with the film-forming polymer and thendispersed in water along with the film-forming polymer. In the lattermethod, it is contemplated that the block copolymer need not be modifiedwith a hydrophilic segment, and instead the affinity of the blockcopolymer for the film-forming vehicle may be relied upon to maintainthe components in a stable dispersion.

The coating compositions of the disclosure may be formulated as eitherone-component (one-package or 1 K) or two-component (two-package or 2K)compositions, as is known in the art.

The adhesion promoter and coating compositions may be coated on anarticle by any of a number of techniques well-known in the art. Theseinclude, without limitation, spray coating, dip coating, roll coating,curtain coating, and the like. Spray coating is preferred for automotivevehicles or other large parts.

The adhesion promoter and optionally chlorinated polyolefin may be addedto a topcoat coating composition in amounts that do not substantiallyalter the gloss of the topcoat. In one application, for example, theolefin-based block copolymer is utilized in a topcoat composition thatproduces a high-gloss cured coating, preferably having a 20° gloss (ASTMD523-89) or DOI (ASTM E430-91) of at least 80 that would be suitable forexterior automotive components.

In another application, the olefin-based block copolymer may be includedin a topcoat or primer composition that produces a low gloss coating,such as for coating certain automotive trim pieces. Typical low glosscoatings have a gloss of less than about 30 at a 60° angle. The lowgloss may be achieved by including one or more flatting agents. Lowgloss primer compositions are often used to coat automotive trim pieces,such as in a gray or black coating. The low gloss primer is preferably aweatherable composition because the low gloss primer may be the onlycoating applied to such trim pieces. In the case of a weatherableprimer, the resins are formulated to be light-fast and the compositionmay include the usual light stabilizer additives, such as hindered aminelight stabilizers, UV absorbers, and antioxidants.

When the coating composition of the disclosure is used as a high-glosspigmented paint coating, the pigment may include any organic orinorganic compounds or colored materials, fillers, metallic or otherinorganic flake materials such as mica or aluminum flake, and othermaterials of kind that the art normally names as pigments. Pigments areusually used in the composition in an amount of 0.2% to 200%, based onthe total solid weight of binder components (i.e., a pigment-to-binderratio of 0.02 to 2). As previously mentioned, adhesion promoterspreferably include at least one conductive pigment such as conductivecarbon black pigment, conductive titanium dioxide, conductive graphite,conductive silica-based pigment, conductive mica-based pigment,conductive antimony pigment, aluminum pigment, or combinations of these,in an amount that makes the coating produced suitable for electrostaticapplications of further coating layers.

The adhesion promoters and coating compositions may be applied atthicknesses that will produce dry film or cured film thicknesses typicalof the art, such as from about 0.01 to about 5.0 mils. Typicalthicknesses for adhesion promoter layers are from about 0.1 to about 0.5mils, preferably from about 0.2 to about 0.4 mils. Typical thicknessesfor primer layers are from about 0.5 to about 2.0 mils, preferably fromabout 0.7 to about 1.5 mils. Typical thicknesses for basecoat layers arefrom about 0.2 to about 2.0 mils, preferably from about 0.5 to about 1.5mils. Typical thicknesses for clearcoat layers or one-layer topcoats arefrom about 0.5 to about 3.0 mils, preferably from about 1.5 to about 2.5mils.

After application to the substrate, the adhesion promoters and coatingcompositions of the disclosure may be heated to facilitate interactionwith the substrate and thus to develop the adhesion of the appliedcomposition to the substrate. Preferably, the coated substrate is heatedto at least about the softening temperature of the plastic substrate.The adhesion promoters and coating compositions are preferably thermallycured. Curing temperatures will vary depending on the particularblocking groups used in the crosslinking agents, however they generallyrange between 160° F. and 270° F. The curing temperature profile must becontrolled to prevent warping or deformation of the TPO substrate orother plastic substrate. The first compounds according to the presentdisclosure are preferably reactive even at relatively low curetemperatures. Thus, in a one embodiment, the cure temperature ispreferably between 225° F. and 270° F., and in another embodiment attemperatures no higher than about 265° F. The curing time will varydepending on the particular components used, and physical parameterssuch as the thickness of the layers, however, typical curing times rangefrom 15 to 60 minutes, and preferably 20-35 minutes. The curingconditions depend upon the specific coating composition and substrate,and may be discovered by straightforward testing.

The coating compositions of the disclosure are particularly suited tocoating olefinic substrates, including, without limitation, TPOsubstrates, polyethylene substrates, and polypropylene substrates. Thecoating compositions may also be used, however, to coat otherthermoplastic and thermoset substrates, including, without limitation,polycarbonate, polyurethane, and flexible substrates like EPDM rubber orthermoplastic elastomers. Such substrates may be formed by any of theprocesses known in the art, for example, without limitation, injectionmolding and reaction injection molding, compression molding, extrusion,and thermoforming techniques.

The materials and processes of the disclosure may be used to form a widevariety of coated articles, including, without limitation, applianceparts, exterior automotive parts and trim pieces, and interiorautomotive parts and trim pieces.

The disclosure is further described in the following examples. Theseexamples are merely illustrative and do not in any way limit the scopeof the disclosure as described and claimed.

EXAMPLES

A control coating composition is prepared having the followingformulation as shown in Table 1; these values are provided prior to theaddition of the amines and other additives. The weight percentages areprovided as the non-volatile content of the coating composition. Allparts are parts by weight unless otherwise noted.

TABLE 1 Weight Percent Component Quantity (non-volatile) Acrylic resin58.20 24.29 Dow Trifunctional Polyester 26.90 22.46 (e.g.,polycaprolactone material) Melamine 5.25 4.39 Polyolefin (modified)86.50 14.44 Conductive carbon black pigment 5.89 4.90 TiO₂ white pigment23.57 19.67 Conductive carbon black pigment 3.93 3.28 Fumed silica 7.866.60 Aromatic 100 solvent 92.40 — Methyl propyl ketone 36.30 — Ethanol8.00 — Aromatic 150 solvent 45.00 — Acid Catalyst 0.22 0.10 Total 400.00100.00

Additional coating compositions are prepared according to the controlformulation as shown in Table 1 that further include either 1% or 2% byweight of dimethylaminoethanol (DMEA) or aminomethylpropanol (AMP) aslisted in Tables 2 and 3. An addition of about 1% by weight of the aminecontaining compound provides about 90% neutralization, while theaddition of about 2% by weight of the amine containing compound providesabout 180% neutralization. Coating compositions are prepared by mixingmaterial together and milling to an appropriate particle size. Wet paintresistivity is recorded as set forth in Table 2. Preferably, the coatingcompositions with such an adhesion promoter provide a wet paintresistivity of less than about 1.5 Mohms, and more preferably less thanabout 1 Mohm. Coatings are then applied to a TPO substrate and dry filmresistivity is evaluated as set forth in Table 3. Preferably, thecoating compositions with such an adhesion promoter provide a dry filmresistivity of less than about 0.02 Mohms, and more preferably less thanabout 0.01 Mohms.

TABLE 2 Amine/Acid Wet Paint Resistivity % Neutralization (Mohms)Control (without amine)  0% 5.1 Adhesion Promoter with  90% 1.4 1% DMEAAdhesion Promoter with 180% 0.9 2% DMEA Adhesion Promoter with  90% 0.71% AMP Adhesion Promoter with 180% 0.4 2% AMP

TABLE 3 Amine/Acid Dry Film Resistivity % Neutralization (Mohms) Control(without amine)  0% 0.03 Adhesion Promoter with 180% 0.015 2% DMEAAdhesion Promoter with 180% 0.01 2% AMP

As represented by the above data, the addition of a small amount ofdimethylaminoethanol and/or aminomethylpropanol dramatically improvesthe paint wet resistivity and the dry film resistivity. Such animprovement in the wet paint resistivity enhances the transferefficiency of the adhesion promoter to a plastic part, while animprovement in the dry film resistivity enhances the transfer efficiencyof the topcoat to the primed part. Additionally, if properly formulated,the amine containing compound may be used as a catalyst in the formationof the coating composition layer. For example, in a two-componenturethane topcoat, the amine could volatize and serve as a catalyst forthe R—NCO (isocyanate)+R′—OH (alcohol) reaction.

The disclosure has been described in detail with reference to variousembodiments thereof. It should be understood, however, that variationsand modifications may be made within the spirit and scope of thedisclosure.

1. A coating composition comprising film forming components and anadhesion promoter, the adhesion promoter comprising an olefin-basedpolymer and at least one amine compound.
 2. A coating compositionaccording to claim 1, wherein the amine compound is selected from thegroup consisting of dimethylaminoethanol, aminomethylpropanol, andmixtures thereof.
 3. A coating composition according to claim 1, whereinthe amine compound is present in an amount from about 1% to about 2% byweight based on total vehicle weight.
 4. A coating composition accordingto claim 1, wherein the olefin-based polymer comprises acarboxyl-functional adhesion copolymer.
 5. A coating compositionaccording to claim 1, wherein the olefin-based polymer includes at leastone functional group selected from the group consisting of hydroxyl,thiol, amide, carbamate, urea, acid, phenol, and combinations thereof.6. A coating composition according to claim 1, wherein the olefin-basedpolymer is present in an amount from about 0.01% to about 30% by weightbased on total vehicle weight.
 7. A coating composition according toclaim 1, wherein the adhesion promoter provides a wet paint resistivityof less than about 1.5 Mohms.
 8. A coating composition according toclaim 7, wherein the adhesion promoter provides a wet paint resistivityof less than about 1 Mohms.
 9. A coating composition according to claim1, wherein the adhesion promoter provides a dry film resistivity of lessthan about 0.02 Mohms.
 10. A coating composition according to claim 9,wherein the adhesion promoter provides a dry film resistivity of lessthan about 0.01 Mohms.
 11. A method of coating a substrate, comprisingapplying a coating composition according to claim 1, wherein the coatingcomposition adhesion promoter is applied as a layer having a thicknessof between about 0.2 to about 0.4 mils.
 12. A method of forming a coatedsubstrate comprising: applying an olefin based polymer adhesion promotercomposition to a substrate, and applying a coating compositioncomprising principal resin and crosslinker to the adhesion promotercomposition, wherein the adhesion promoter composition comprises atleast one amine containing compound in an amount between about 1% toabout 2% by weight based on total vehicle weight and has functionalitythat does not react with the principal resin or crosslinker of thecoating composition.
 13. A method according to claim 12, wherein theolefin based polymer comprises a carboxyl functional adhesion copolymer.14. A method according to claim 12, wherein the amine containingcompound is selected from the group consisting of dimethylaminoethanoland aminomethylpropanol.
 15. A method according to claim 12, comprisingusing the amine containing compound as a catalyst in the formation ofthe coating composition.
 16. A method of improving the transferefficiency of a topcoat layer to a primed component, the methodcomprising: applying a carboxyl functional olefin based polymercomposition to a substrate to provide a primed component, and applying acoating composition comprising principal resin and crosslinker to theprimed component to form a topcoat layer, wherein the carboxylfunctional olefin based polymer is neutralized with at least one aminecontaining compound to form a salted carboxyl functional polymer.
 17. Amethod according to claim 16, wherein the amine containing compound isselected from the group consisting of dimethylaminoethanol,aminomethylpropanol, and combinations thereof.
 18. A method according toclaim 16, comprising using the amine containing compound as a catalystin the formation of the coating composition.
 19. A method according toclaim 16, wherein the amine containing compound is present in an amountbetween about 1% to about 2% by weight based on total vehicle weight.20. A method according to claim 16, wherein the salted carboxylfunctional polymer is used to form a waterborne adhesion copolymer.